“Bulldozers” or “dozers”, as those terms are used herein, refer to crawler-tractors that are equipped with a blade for scraping the ground or pushing material along the ground. The blade is pivotally connected to the crawler-tractor chassis such that they can pivot up and down. Blade controls are provided to the operator in the cab of the vehicle. These controls permit the operator raise and lower the blade with respect to the chassis of the crawler-tractor. One of the most common uses for blades on bulldozers is to level or otherwise contour ground for construction of houses, buildings, parking lots, and roads. Often the terrain that the bulldozer starts working is quite uneven and rough. As it passes over this rough terrain, the bulldozer chassis often begins to pitch.
When the chassis pitches up and down, the blade pitches as well. As the blade pitches up the blade digs the earth shallower. As the blade pitches down, it digs into the earth deeper, duplicating in the earth the fluctuations of the dozer chassis as it pitches over the rough terrain. Instead of evenly leveling the terrain, a bulldozer tends to reproduce the very rough terrain over which it drives.
A skilled operator can reduce the pitching of the blade by anticipating the pitching of the chassis and moving the blade in the opposite direction. By manually pitching the blade in a direction opposite to the direction the chassis pitches and at exactly the same time, the operator can grade the terrain more level than if the blade merely pitches with the chassis. This ability to anticipate the motion of the chassis and pitch the blade in the opposite direction takes a good deal of skill, and that skill can only be acquired through experience.
Even a talented driver, however, cannot travel at full speed over rough terrain, but must reduce his speed to accommodate the pitching of the dozer blade as the dozer chassis pitches up and down as it travels over the ground.
The process of leveling the ground using a bulldozer blade is called “grading”. Systems for automatically grading the ground have been devised that use sensors mounted on a bulldozer blade and laser light sources located at the corners of a field to be graded. These light sources transmit light to the sensors attached to the bulldozer blade.
As a bulldozer equipped with these systems pitches backward or forward, the blade begins to pitch up or down, causing the light falling on the sensor to fall or rise, respectively. A controller coupled to the sensor controls blade pitching by raising and lowering the blade to keep it in the same position with respect to the ground.
This system, however, requires the careful placement and adjustment of light sources and an unobstructed view of the bulldozer blade.
What the inventors have discovered is that for many applications this laser-guided whole-field system is overkill. Many operators, especially novice operators, would be significantly benefited by a system that merely monitors bulldozer pitching as it goes over rough terrain and keeps the blade in a relatively constant position and at a relatively constant height as the chassis of the bulldozer pitches forward and backward.
What is needed, therefore, is a system for reducing dozer blade pitching as the dozer chassis pitches. What is also needed is a dozer that has a system for reducing dozer blade pitching. What is also needed is a system for keeping the dozer blade at a relatively constant height and at a relatively constant position as the chassis of the tractor-crawler pitches. What is also needed is a system that at least partially relieves the operator of the burden of manually raising and lowering the blade as the vehicle pitches while traveling over the ground. What is also needed is a system that permits the operator to grade faster by automatically controlling blade pitching. What is also needed is a system that automatically controls blade pitching faster than an operator can manually control blade pitching. It is an object of this invention to provide such system and bulldozer.